The present invention relates generally to air curtains for separating a first environment from a second environment. The method of the present invention may be advantageously applied to refrigerated display merchandisers of the type used in supermarkets, mini-marts, convenience stores and other commercial establishments for displaying and merchandising refrigerated or frozen products for sale, wherein an air curtain separates the open-front, product display area from the ambient store environment.
Refrigerated display merchandisers, also commonly referred to as display cases, having open front display regions are commonly used in supermarkets, mini-marts, convenience stores and other commercial establishments for displaying and merchandising refrigerated or frozen products for sale. The open front nature of such display cases permits the consumer to simply reach into the product display region to select and remove a product for purchase without the inconvenience of needing to open a door to access the product. Customarily, a curtain of cold refrigerated air is passed downwardly at a relatively high velocity across the open front of the display case to form an invisible boundary between the product display region and the region of the store in front of the display case. This air curtain not only helps retain cool refrigerated air within the product display region of the display case, thereby cooling the display product on the shelves of the display case, but also functions to isolate, to a certain extent, the product display region from the ambient air within the store. Ambient air that does enter into open product display region undesirably causes increased energy consumption by increasing the cooling demand on the refrigeration system associated with the display case. Further, such ambient air may also cause a local temperature rise within the product display region sufficient to result in an undesirable rise in product temperature that could adversely impact upon product quality.
A problem encountered with when passing a curtain of refrigerated air downwardly across the open front of the product display region of the display case lies in the entrainment of ambient air into the stream of refrigerated air forming the air curtain. Turbulence exists at the boundary between the relatively high velocity curtain air and the generally quiescent ambient air lying in front of the display case. As a result of such turbulence, some ambient air is undesirably entrained into the air curtain. Multiple air curtain display cases have been developed in the prior art to address this entrainment problem. For example, display cases having two adjacent, parallel, but independently generated, air curtains of refrigerated air are common in the art. Typically, such as disclosed by Maehara in U.S. Pat. No. 4,633,677, the outermost air curtain has a slightly higher temperature than the innermost air curtain, so as to protect the colder innermost air curtain from the impact of ambient air entrainment. However, such designs do not completely eliminate the intrusion of ambient air into the refrigerated air curtain.
Also, it is well known in the art to establish a third air curtain of relatively high velocity ambient air outwardly of one or two refrigerated air curtains as a means of reducing entrainment of ambient air from the store into the refrigerated air curtains. Abraham, in U.S. Pat. No. 4,267,706, discloses establishing an ambient air curtain outwardly of an innermost refrigerated air curtain, with the outer ambient air curtain being directed downwardly parallel to and adjacent to the inner refrigerated air curtain.
Beckwith et al, in U.S. Pat. Nos. 3,648,482 and 3,850,003, MacMaster et al, in U.S. Pat. No. 3,827,254 and Roberts, in U.S. Pat. Nos. 5,345,778 and 5,357,767, each disclose establishing an ambient air curtain outwardly of a pair of refrigerated air curtains. The curtain closest to the product display region of the display case is coolest, while the center curtain is at a temperature slightly warmer than the innermost curtain, but substantially cooler than the outermost ambient air curtain. The center curtain of warmer refrigerated air serves to buffer the innermost colder refrigerated air curtain from warm air intrusion from the outermost ambient air curtain. The outermost curtain of ambient air is directed substantially vertically downwardly, either parallel to and adjacent the center air curtain or slightly inwardly toward the center air curtain, so as to preclude refrigerated air from the center and innermost refrigerated air curtains from spilling out of the product display region of the display case. The outermost ambient air curtain itself ideally spills into the store near the base of the display case so as to not be drawn into the air return inlets through which the refrigerated air curtains return to the evaporator compartment. Although generally quite effective in reducing intrusion of ambient air into the colder innermost refrigerated air curtain, some intrusion into the center refrigerated air stream will occur.